Pre-chamber

ABSTRACT

A pre-chamber is provided. In one embodiment, the pre-chamber is part of a two-stroke combustion engine having a cylinder head with a sparkplug receptacle that has a generally frustoconical shape, and the pre-chamber is coupled to the sparkplug receptacle. The pre-chamber may include a cooling jacket with a generally frustoconical shape and a combustion chamber having an upper zone and a lower zone, which may be narrower than the upper zone.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/036,041, entitled “Pre-Chamber”, filed on Mar. 12, 2008, which isherein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to combustion engines. Moreparticularly, the present invention relates to pre-chambers forcombustion engines.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Engine design has changed in response to environmental regulations, asgovernment agencies enforce increasingly stringent limits on engineemissions. Starting in 2008, the United States Environmental ProtectionAgency will further restrict the levels of nitrogen oxides (NOx), carbonmonoxide (CO), and non-methane hydrocarbon (NMHC) emitted by certaintypes of combustion engines. To meet these requirements, many types ofengines now include pre-chambers. These devices ignite the fuel-airmixture inside the engine's cylinders with a flame from secondarycombustion inside the pre-chamber. During the compression stroke of theengine, the pre-chamber is loaded with a relatively rich fuel-airmixture. To initiate combustion, this richer fuel-air mixture is ignitedin the pre-chamber, rather than ignition being initiated by directlyigniting the leaner fuel-air mixture in the cylinder. The resultingflame propagates from the pre-chamber into the cylinder, combusting thefuel in the cylinder more completely, and more rapidly, producing fewerundesirable emissions.

Many engines built prior to the adoption of recent environmentalregulations do not include pre-chambers, and generally do not addressemissions-related concerns. As a result, there is a large installed baseof engines that may not satisfy newer emissions regulations. Replacingthese installed engines with newer designs that include pre-chambers toreduce emissions would be expensive. Accordingly, to control emissions,for instance, it would be useful to find a way to retrofit the olderengines with pre-chambers. Older engines, however, often do not havesufficient space above the cylinder heads to receive a pre-chamber, asthe cylinder heads were designed with relatively small sparkplug wellsto couple directly to spark plugs, which are typically smaller thanpre-chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective view of a cylinder head and a pre-chamber inaccordance with an embodiment of the present technique;

FIG. 2 is a cross-section view of the cylinder head of FIG. 1;

FIG. 3 is a perspective view of the pre-chamber of FIG. 1,

FIGS. 4-6 are cross-section views of the pre-chamber of FIG. 1; and

FIG. 7 illustrates a gas-compression system that includes the cylinderhead and pre-chamber of FIG. 1

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” “said,” and the like, areintended to mean that there are one or more of the elements. The terms“comprising,” “including,” “having,” and the like are intended to beinclusive and mean that there may be additional elements other than thelisted elements. The use of “top,” “bottom,” “above,” “below,” andvariations of these terms is made for convenience, but does not requireany particular orientation of the components.

FIG. 1 illustrates an example of a cylinder head 10 and a pre-chamber12. As explained below, the cylinder head 10 is representative of astyle of cylinder head used on two-stroke engines that were not designedto include a pre-chamber. The pre-chamber 12, however, is configured tocouple to this style of cylinder head and retrofit older engines,lowering the emissions of these engines and potentially extending theiruseful life. The pre-chamber 12 is described in greater detail below,after describing features of the cylinder head 10.

The exemplary cylinder head 10 has a generally right cylindrical shapethat is generally concentric about a central axis 14, and the head 10includes a coolant inlet 16, a gas inlet 18, a plurality of bolt holes20, and a sparkplug receptacle 22. The cylinder head 10 may be made ofcast or machined steel, or other appropriate materials; and it may beconfigured to couple to a cylinder of a two-stroke engine.

The cylinder head 10 is configured to receive several fluid flows. Asexplained below with reference to FIG. 2, the cylinder head 10 mayinclude generally hollow sidewalls that are in fluid communication withthe coolant inlet 16 to enable circulation of a coolant. The gas inlet18 is shaped to couple to a gas-injection valve that injects fuel, suchas methane or other constituents of natural gas, into the cylinder. Theillustrated gas inlet 18 is generally centrally located on the cylinderhead 10 and is generally concentric about the central axis 14.

The bolt holes 20 are generally evenly distributed around the outerradius of the cylinder head 10 and extend through the cylinder head 10generally parallel to the central axis 14. Bolts extending through thebolt holes 20 secure the cylinder head 10 to a cylinder, which may alsobe generally concentric about the central axis 14.

The illustrated cylinder head 10 includes two sparkplug receptacles 22that are generally reflectively and rotationally symmetric to eachother. Although only one of the illustrated sparkplug receptacles 22 isconnected to a pre-chamber 12, a pre-chamber 12 may be connected to eachsparkplug receptacle 22. The sparkplug receptacles 22 are configured toreceive a sparkplug and position an electrode of the sparkplug insidethe cylinder. A threaded aperture 24 at the base of each sparkplugreceptacle 22 is shaped to mate with external threads on the sparkplug.Other embodiments may include more or fewer sparkplug receptacles 22 orengagement mechanisms.

Additional details of the sparkplug receptacles 22 and other features ofthe cylinder head 10 are illustrated by FIG. 2. Each sparkplugreceptacle 22 includes a generally planar base 26, a frustoconicalportion 28, and a chamfer 30. The base 26 and the frustoconical portion28 are generally concentric about an axis 32, which may be at an angle34 with respect to the central axis 14. The angle 34 may be between 5and 25 degrees, e.g., between 12 and 18 degrees or generally equal to 15degrees. The frustoconical portion 28 may have a lower diameter 36 thatis between 1 and 3 inches, e.g., between 1.5 and 2 inches, and an upperdiameter 38 that is between 2 and 4 inches, e.g., between 3 and 3.5inches. The distance along the axis 32 between the upper diameter 38 andthe lower diameter 36 may be between 1 and 3 inches, e.g., between 2 and2.5 inches.

FIG. 2 illustrates several other interior features of the cylinder head10. The coolant inlet 16 leads to a chamber 40 (e.g., an annular coolantpassage) that extends around the cylinder head 10. The chamber 40 is influid communication with a plurality of apertures 42 that connect to acooling jacket in sidewalls of the cylinder. The bottom, interior of thecylinder head 10 defines a generally dome shaped volume 44 that forms atop part of the main combustion chamber. The portion of the cylinderhead 10 adjacent the dome shaped volume 44 is cooled by coolantcirculating through the chamber 40.

FIG. 3 illustrates details of the pre-chamber 12. In this embodiment,the pre-chamber 12 includes a sparkplug 44, a coolant inlet 46, acoolant outlet 48, a fuel valve 50, and a body 52. The sparkplug 44includes an electrical interface 54 for connecting the sparkplug 44 to apower source and a hexagonal tool interface 56 for threading thesparkplug 44 to the body 52. The coolant inlet 46 and the coolant outlet48 include a lower nut that couples them to the body 52 and an upper nutfor coupling to coolant hoses. The fuel valve 50 includes a threadedfuel inlet 58 and a bracket 60 for mounting the coolant hoses. The fuelvalve 50 may be a check valve that enables flow in one direction intothe pre-chamber 12 and impedes flow in the opposite direction out of thepre-chamber 12.

The body 52 includes a clamping member 62, a cooling jacket 64, and atip 66. In this embodiment, the clamping member 62 is biased against thecooling jacket 64 by a plurality of bolts 68 that are threaded to thecooling jacket 64, as discussed further below with reference to FIG. 4.The clamping member 62 has a generally flat and generally circular topface 70 and apertures 72 and 74 that extend through the top face 70 forreceiving the sparkplug 44 and the fuel valve 50, respectively.

The cooling housing 64 has a generally frustoconical shape that iscomplementary to the sparkplug receptacle 22 described above. Agenerally annular flange 76 mates with the clamping member 62, and aseal 78 (e.g., annular seal) is disposed around the tip 66 adjacent thenarrower portion of the cooling housing 64. The seal 78 may be made ofor include a metal, such as copper, or other appropriate materials. Thetip 66 defines a generally right cylindrical volume and extends from thenarrower portion of the cooling housing 64. The tip 66 has externalthreads that are complementary to the threads in the aperture 24 forsecuring the pre-chamber 12 to the cylinder head 10 (FIGS. 1 and 2).

FIG. 4 illustrates a cross-section of the pre-chamber 12. Asillustrated, the clamping member 62 is connected to the tip 66 by aninner body 80. An interior of the inner body 80 defines a combustionchamber (i.e., preliminary or secondary to a main combustion chamber)with an upper zone 82, an intermediate zone 84, and a lower zone 86. Theupper zone 82 generally defines a segment of a sphere that is greaterthan a hemisphere. The lower zone 86 generally defines a segment of asphere that is less than a hemisphere and has a smaller diameter thanthe sphere segment defined by the upper zone 82. The intermediate zone84 has a generally frustoconical shape that is generally tangent to thewalls of the upper zone 82 and the lower zone 86. A geometricalconfiguration with the lower zone 86 smaller than the upper zone 82facilitates fitting the pre-chamber 12 within the generallyfrustoconical sparkplug receptacles 22 (FIGS. 1 and 2), whilemaintaining a certain volume of the combustion chamber defined by zones82, 84 and 86. In some embodiments, the volume of the combustion chamberincluding the zones 82, 84 and 86 is between 1% and 3% of the sweptvolume of the cylinder coupled to the head 10, e.g., between 1.5% and2%. As used herein, the term “swept volume” refers to the volume throughwhich the top surface of the piston sweeps during a stroke in the maincombustion chamber.

The combustion chamber is in fluid communication with several componentsof the pre-chamber 12. The upper zone 82 is in fluid communication witha generally cylindrical volume 88 that receives an electrode 90 of thesparkplug 44. The volume 88 is considered part of the combustion chambervolume, along with the zones 82, 84, and 86. A passage 92 places thefuel valve 50 in fluid communication with the upper zone 82. In thisembodiment, the passage 92 is angled relative to the surface of theupper zone 82, i.e., the passage 92 is not normal to the surface of theupper zone 82. The passage 92 may be at an angle relative to thissurface (or a tangent line at the area of intersection) that is between40 and 50 degrees. Another passage 94 placed in the lower zone 86 is influid communication with the exterior of the tip 66 and the interior ofthe cylinder (i.e., the main combustion chamber defined by apiston-cylinder assembly). The passage 94 includes an angled portion 96that is angled relative to the surface of the lower zone 86. The angledportion 96 may be at an angle relative to this surface that is between10 and 20 degrees. The passages 92 and 94 are generally parallel to acommon plane, but in other embodiments, they may extend generallyparallel to different planes.

The inner body 80 is secured to the clamping member 62 by a weld 98. Insome embodiments, these components 80 and 62 are cast and machinedseparately and then welded together. In other embodiments, the innerbody 80 and clamping member 62 may be integrally formed as a singlecomponent. The tip 66 may also be welded or integrally formed with theinner body 80.

The inner body 80 includes a shoulder 100 that biases a seal 102 (e.g.,annular seal) against a shoulder 104 of the cooling jacket 64. To biasthese components, the bolts 68 compress the clamping member 62 and theinner body 80 against the cooling jacket 64 through the shoulders 100and 104. The compression of the inner body 80 and clamping member 62 isbalanced by tension applied to the cooling jacket 64 by the bolts 68 andthe shoulder 100. In this embodiment, the inner body 80 is not threadedto the cooling jacket 64, and the threaded connections to the bolts arenear a distal portion of the pre-chamber 12, away from the heat of thecylinder. Positioning the threaded connections away from the cylinder(i.e., the main combustion chamber defined by a piston-cylinderassembly) is believed to keep the threaded components cooler and reducethe likelihood of the threaded components seizing to one another due tothermal cycling.

The cooling jacket 64 cooperates with an exterior of the inner body 80to define an outer volume 106 (e.g., an annular coolant passage)configured to circulate a coolant. The outer volume 106 is sealed by theseal 102 and an O-ring 108 disposed about the clamping member 62. Theseal 102 may include a graphite gasket or other appropriate materials.The O-ring 108 may be made of a less expensive material with a lowertemperature rating than the seal 102. For example, the seal 102 may berated for temperatures as high as 800 to 1000 degrees F., and the O-ring108 may be or include Cal Res, a fluoro-carbon, or other appropriatematerial rated for temperatures as high as 400 or 600 degrees F.

FIG. 5 illustrates a cross-section that is generally orthogonal to thecross-section of FIG. 4. As illustrated by FIG. 5, the coolant inlet 46and the coolant outlet 48 are in fluid communication with the outervolume 106 through passages 110 and 112. These passages 110 and 112circulate coolant through the outer volume 106, cooling the inner body80 and removing heat from combustion within the inner body 80.

In this embodiment, the clamping member 62 and the inner body 80 may beremoved from the cooling housing 64 for maintenance. Coolant circulatingthrough the pre-chamber 12 may form deposits in the outer volume 106.Removing the clamping member 62 and the inner body 80 facilitatescleaning these deposits and potentially extends the useful life of thepre-chamber.

As mentioned above, the pre-chamber 12 is generally complementary to thesparkplug receptacle 22. To fit within the sparkplug receptacle 22 ofcertain engines, the pre-chamber 12 has a generally frustoconical shapewith a lower width 114 that is less than 1.8 inches, e.g., less than orgenerally equal to 1.5 inches, and an upper width 116 that is less than5 inches, e.g., generally equal to or less than 4 inches. The height 118of the body 52 may be less than 5 inches, e.g., generally less than orequal to 4.3 inches.

FIG. 6 illustrates fluid flow in the pre-chamber 12. In operation, thepre-chamber 12 is coupled to the cylinder of a two-stroke engine. Duringthe compression stroke, air flows into the combustion chamber from thecylinder through the aperture 94, as illustrated by arrow 120, and fuelflows into the combustion chamber through the passage 92, as illustratedby arrow 122. As mentioned above, these passages 92 and 94 are angled toestablish a swirling flow, as illustrated by arrow 124. The swirlingflow may swirl about one axis or two axes, e.g., it may spiral,depending on whether the passages 92 and 94 are generally co-planar. Inthis embodiment, the flow generally rotates about one axis that isgenerally perpendicular to the cross-section of FIG. 6. The swirlingflow 124 is believed to be generally laminar and is believed to enhancemixing of the fuel and air, boosting combustion.

Near the top of the piston's stroke through the cylinder, i.e., top deadcenter (TDC), the sparkplug 44 creates a spark in the pre-chamber, andthe swirling air-fuel mixture is ignited. The resulting flame propagatesthrough the passage 94 into the cylinder and ignites the larger volumeof fuel-air mixture within the cylinder. The flame produced by thepre-chamber 12 is believed to yield more complete combustion within thecylinder and reduce emissions from the engine.

FIG. 7 illustrates an example of a compression system 126 that includesthe pre-chamber 12 described above. The system 126 includes anatural-gas well 128, an engine 130 retrofitted with one or more of thepre-chambers 12, a compressor 132, and a pipeline, storage, or otherfluid destination 134. The gas well 128 may be a subsea or a surfacenatural gas well. The engine 130 may be a two-stroke combustion enginehaving between 40 and 800 hp, e.g., between 40 and 200 hp.

In operation, natural gas flows from the gas well 128 to the compressor132, as illustrated by arrow 136. A portion of this flow is diverted tothe engine 130, as illustrated by arrow 138. The diverted flow of 138may be conditioned by removing moisture or changing the gas pressurebefore being introduced to the engine 130. A small portion of thediverted gas 138 flows into the pre-chamber 12 and the rest of thediverted gas 138 flows into the cylinders of the engine 130. The engine130 combusts the diverted fuel 138 by igniting the fuel in thepre-chambers 12, as described above, and drives a shaft 140 or othermechanical linkage that powers the compressor 132. The compressor 132compresses the flow 136 from the gas well 128 and produces an outletflow 142 at a higher pressure.

Because the pre-chamber 12 described above is compatible with certaintypes of engines that were not designed to include pre-chambers, theengine 130 may be an older design, e.g., an engine that was in existenceor designed before 1995, 2000, or 2008. Retrofitting older engines withpre-chambers is believed to reduce the emissions and enhance theefficiency of these older engines, bringing the engines closer tosatisfying newer emissions regulations.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A device comprising: a two-stroke combustion engine comprising: acylinder head having a sparkplug receptacle, wherein the sparkplugreceptacle has a generally frustoconical shape; and a pre-chambercoupled to the sparkplug receptacle, wherein the pre-chamber comprises:a cooling jacket that defines a generally frustoconical shape; and acombustion chamber comprising an upper zone and a lower zone, whereinthe upper zone is wider than the lower zone.
 2. The device of claim 1,wherein the sparkplug receptacle is generally angled relative to acentral axis of the cylinder head.
 3. The device of claim 1, wherein thecylinder head comprises two spark plug receptacles that are generallyreflectively symmetric.
 4. The device of claim 1, wherein cooling jacketis not threaded to the combustion chamber.
 5. The device of claim 1,wherein the upper zone generally defines a segment of a sphere.
 6. Thedevice of claim 1, wherein the lower zone generally defines a segment ofa sphere.
 7. The device of claim 1, wherein the upper zone is joined tothe lower zone by a generally frustoconical zone.
 8. A devicecomprising: a pre-chamber comprising: a removable inner body comprising;a first shoulder; and a tip extending from the first shoulder, whereinthe tip is configured to thread into a threaded aperture of a sparkplugreceptacle; a cooling housing disposed at least partially around theremovable inner body, wherein the cooling housing comprises a secondshoulder biased against the first shoulder; a clamping member coupled tothe removable inner body and coupled to the cooling housing by athreaded connection, wherein the threaded connection is disposed at adistal portion of the pre-chamber away from the tip.
 9. The device ofclaim 8, wherein the removable inner body is biased in compression andthe cooling housing is biased in tension by the clamping member.
 10. Thedevice of claim 8, wherein the removable inner body comprises acombustion chamber having a zone that generally defines a segment of asphere.
 11. The device of claim 10, wherein the segment of the sphere isgreater than a hemisphere.
 12. The device of claim 8, wherein theremovable inner body comprises: a combustion chamber; and a fuel passagethat is generally tangent to the combustion chamber.
 13. The device ofclaim 12, wherein the tip comprises a passage that is generallyco-planar with the fuel passage.
 14. The device of clam 13, wherein thepassage comprised by the tip has a bent portion that is generallytangent to the combustion chamber.
 15. A system, comprising: an enginebuilt before 2008; a pre-chamber coupled to the engine, wherein thepre-chamber has a generally frustoconical shape; and a gas well coupledto the engine.
 16. The system of claim 15, wherein the engine isconfigured to receive fuel from the gas well.
 17. The system of claim15, wherein the pre-chamber has a combustion chamber that comprises: anupper zone that generally defines a segment of a sphere; a lower zonethat generally defines a segment of a sphere; and a frustoconicalportion that extends between the upper zone and the lower zone.
 18. Thesystem of claim 15, wherein the engine is a two-stroke engine configuredto combust methane.
 19. The system of claim 15, comprising a compressorcoupled to both the gas well and the engine, wherein the compressor isconfigured to compress a gas from the gas well with mechanical energyreceived from the engine.
 20. The system of claim 15, wherein thepre-chamber comprises: a cooling housing in tension; and a inner body incompression.